High frequency apparatus



Nov. 10, 1959 J. COLLARD 2,912,619

HIGH FREQUENCY APPARATUS Filed April 19, 1955 FIG. 2.

. HIGH FREQU-ENCY APPARATUS John Collard, Hammersinitli, London,England, assignor to Electric 8: Musical Industries Limited, Hayes,Middle'sex, England, a company of Great Britain Application April19,1955, Serial No. 502,336 Claims priority, application Great Britain-April 22, 1954 10 Claims. (Cl. 315-39) The present invention relates tohigh frequency apparatus in which a high frequency is set up and theinvention being particularly but not exclusively concerned withmeasuring the power propagated along waveguides.

For the purpose of measuring power it has been a commonpractice in thepast to employ germanium crystals as'rectifiers but such arrangementssuffer from the objection that the crystals are easily damaged byoverload conditions. An object of the present invention is to providesimple and convenient apparatus for power measurement and other purposeswhich does not employ a crystal rectifier. v V

According to the present invention there is provided high frequencyapparatus in which a thermionic electron discharge device is arrangedwithin the field set up by said apparatus, said device including acathode and an anode which is influenced in potential only by saidalternating electric field and which is large compared with said cathodeand disposed in relation to said cathode so that said high frequencyfield existing in the space between said cathode and anode becomesprogressively weaker towards said anode, whereby electrons emitted bysaid cathode and accelerated therefrom by said field continue tomove-towards said anode despite reversal of said field. As applied tothe measurement of power propagated along a waveguide said thermionicelectron discharge device-maytake the form of a small thermionic diodein an evacuated glass tube which is arranged within the waveguide andwith the cathode of the diode disposed coaxially with the axis of thewaveguide. Such an arrangement is convenient not only for themeasurement of power but is convenient also for the detection, mixingand modulation of oscillations.

In order that the invention may be more clearly understood the same willnow be described by way of example with reference to the accompanyingdrawing, in which:

Figure 1 shows an arrangement in accordance with the invention,

Figure 2 shows a side elevation of a thermionic diode for use inaccordance with the invention, and

Figure 3 illustrates the manner of mounting the diode shown in Figure 2in a waveguide.

Referring to Figure l, the invention is shown as applied to highfrequency apparatus in the form of a waveguide. The waveguide is ofrectangular cross-section having broad walls as indicated by thereference numerals 1 and '1' and narrow walls indicated by the numerals2 and 2', the guide being excited so that a field of H type is set upwithin it. With a field of this type the electric vector is normallyparallel to the narrow walls and there is located in a region where thefield is a maximum, namely, at the centre of the guide 3, a thermionicdiode of which the dotted line indicates the evacuated glass envelopeand reference numerals 4 and 5 indicate the cathode and anoderespectively. The cathode is in the form of a filament extendingcoaxially with the axis of the guide and the anode is of elongatedarcuate form in cross-section and located on the side of the cathodetowardsone of the broad walls of the waveguide. As will be seen theanode 5 subtends an angle with respect to'the cathode 4 which issubstantially less than 360.

The diode is shown in greater detail in Figure 2 of the drawings and asshown therein, the diode comprises a glass tubular envelope 6 which in atypical example may be approximately 1%" long and A" in diameter. The

anode 5 is mounted between a pair of mica spacers 7 and 8 between whichis also arranged the filament 4. The two leads for the filament 4 areindicated at 9 and 10 and the lead for the anode at 11. The filament 4should be as small in diameter as possible and is preferably of thedirectly heated type. The anode 5 in a typical example may have a radiusof A2" and the cathode 4 is disposed at the radial point of the anode.The anode should be a half wavelength long at the frequency of theelectro-magnetic waves propagated through the waveguide.

Figure. 3 of the:drawings illustrates the manner of mounting the diodein the waveguide and as shown, the leads 9, 10 and 11 are arranged tosupport the diode in the waveguide, the leads being bent so that theyare disposed at right angles to the electric field set up within thewaveguide and pass through apertures in one of the walls 2 and 2' of thewaveguide, two of the apertures being indicated in Figure 3 at 12 and13, the leads being suitably insulated from the Waveguide.

As shown in Figure 1, the presence of the cathode 4 results in theconvergence upon it of those lines of electric force presentin theregion of the diode 3 and in consequence the field existing in the spacebetween the cathode 4 and the anode 5 of the diode is of radial form sothat the field between cathode and anode becomes progressively weakertowards the anode. The weakening of the field towards the anode isessential to the operation of the invention and with this form of fieldit will be seen that while an electron may be accelerated by the fieldstrongly away from the cathode upon emission it is not possible for thereversal of the field to bring the electron to rest or return it towardsthe cathode since the electron will by that time have reached a pointwhere the field is too weak for this purpose. Thus despite reversals ofthe field the electron retains a forward velocity and continues to movetowards the anode so that the anode continues to charge up bytheaccession of emitted electrons until its potential is such that onthe average as many electrons are driven off as are being received. Thepotential of the anode in this way is a function of the power propagatedalong the guide.

As stated above, the invention may be employed as a signal detector andthe manner of operation when so employed is similar to that describedabove as applied to the measurement of power, and the arrangement is ofsimilar construction. The same form of apparatus may be employed for thepurpose of mixing and here it is merely necessary to arrange that twofields of different frequencies are introduced into the waveguide so asto be effective upon the diode.

Although the invention has been described above as applied to arectangular waveguide it will be appreciated that the invention can beemployed in any device in which a high frequency field exists, such asin coaxial lines, cavity resonators and other devices where the electricfield can converge onto the cathode of the diode.

What I claim is:

1. High frequency apparatus including a wave-guide adapted to be excitedto set up an alternating electric field and a thermionic electrondischarge device arranged Within said field, saiddevice including acathode and an anode spaced from said cathode and which is influenced inpotential only by said alternating electric field and which is largecompared with said cathode and subtends an angle with respect to saidcathode which is substantially less than 360, to expose said cathode tosaid field, the shape of said anode and said spacing and" angle beingchosen to cause the field in the space between said cathode and anode tobecome progressively weaker towards said anode thereby to causeelectrons emitted by said cathode and accelerated therefrom by saidfield to continue to move towards said anode despite reversals of saidfield.

2. High frequency apparatus according to claim 1, wherein said anode isof arcuate form in cross-section with the concavity of said' anodefacing said cathode.

3'. High frequency apparatus according to claim 1, wherein said cathodeis of filamentary form and said an ode is of said arcuate elongated formwith the concavity of said anode facing said cathode.

4. A high frequency transmission line adapted to transmit an alternatingelectric field and a thermionicelectron discharge device arranged withinsaid field, said device including a cathode and an anode spaced fromsaid cathode and which is influenced in potential only by saidalternating electric field and which is large compared with said cathodeand subtends an angle with respect to said cathode of substantially lessthan 360, to expose said cathode to said field, the shape of said anodeand said spacing and angle being chosen to cause the field between saidcathode and anode to become progressively weaker towards said anodethereby to cause electrons emitted by said cathode and acceleratedtherefrom by said field to continue to move towards said cathode despite reversals of said field.

5. A transmission line according to claim 4, wherein said anode is ofarcuate form with the concavity of said anode facing said cathode.

6. A transmission line according to claim 4 wherein said cathode is offilamentary form with its axis substantially parallel to the axis ofsaid line and said anode is of arcuate elongated form with itslongitudinal axis substantially parallel to the axis of said line andwith the concavity of said anode facing said cathode.

7. A waveguide of rectangular form in cross-section adapted to beexcited to said up an alternating electric 4% field with the lines ofsaid field substantially parallel to the narrow walls of said'waveguide,and' a thermionic electron discharge device arranged within said field,said device including a cathode and an anode spaced from said cathodeand which is influenced in potential only by said alternating electricfield; and which is large com pared with said cathode and subtends anangle with re* spect to said cathode of substantially less: than 360, to

expose said cathode to said field thelshape of said an-,

ode and said spacing and. angle being chosentocause the field betweensaid cathode and anodeto. becomeprw gressively weaker towards said anodethereby to cause electrons emitted by said cathode and. acceleratedtherefrom by said field to continue to movetowardssaid,catlr ode despitereversals of said field.

8. A waveguide according. to claim 7, wherein said anode is disposed onthe side of said cathode facing one of the broad walls of saidwaveguide.

9'. A waveguide according to claim 7; whereinsaid anode is of arcuateform in cross-section and is disposed on the side of said cathode facingone ofthe broad; walls of said waveguide.

10. A waveguide according to claim 7', wherein said cathode is offilamentary form with its axis substantially parallel to the axis ofsaid waveguide and said anodeisof arcuate elongated form with itslongitudinal axis substantially parallel to the axis of said waveguideand'with,

the concavity of said anode facing said cathode and disposedon the sideof said cathode facing one of the broad walls of said waveguide.

References Cited in the'file ofthis patent UNITED STATES PATENTS

